1.Field of the Invention
This invention relates to a twin-beam weaving machine using a pair of left and right warp beams to weave a textile fabric having a large breadth and, more particularly, to a warp feed controller of a twin beam weaving machine designed to reliably prevent the occurrence of a wale streak defect in a central portion of a fabric.
2. Description of the Related Art
Weaving machines capable of weaving a textile fabric having a large breadth by a pair of left and right warp beams have been known as twin beam weaving machines.
In such twin beam weaving machines, if tensions of warp yarns from the warp beams are unbalanced, a noticeable wale streak occurs in a warp boundary portion, i.e., a central portion of the fabric. Twin beam weaving machines therefore require a special means devised to balance the tensions of warp yarns fed from the warp beams (for example, as in the weaving machine disclosed in Japanese Utility Model Laid-Open No. Sho 61-180184.
For example, the difference between two groups of warp yarns from the warp beams may be canceled by detecting the tensions of the warp yarns fed from the warp beams with tension detectors when the left and right beams are driven through a differential gear mechanism connected to a common drive shaft, and by braking one or both the warp beams on the basis of tension signals from the tension detectors. That is, the tension detectors are disposed at positions corresponding to two side end portions of a fabric, the tension signals from the tension detectors are compared by a comparison control means, and the braking force of brakes interposed between the differential gear mechanism and the warp beams are controlled according to the result of the comparison.
This prior art entails the problem of difficulty in completely preventing occurrence of a wale streak in a central portion of a fabric, because the tensions of warp yarns from the warp beams are measured at positions corresponding to two side end portions of the fabric.
That is, in general, the tensions of warp yarns are not always constant in the widthwise direction of the warp beams, they are liable to be smatter in side end portions of a fabric and to be larger in a central portion of the fabric, and the magnitude of variation in tension ordinarily disperses with respect to warp beams. This is because weft yarns tend to be looser in side end portions of the fabric so that the amount of consumption of warp yarns is smaller, because dispersions of slashed states and dispersions of the wound hardness in a preparatory step with respect to warp beams are not negligible, because mechanisms for applying tensile forces to warp yarns from the left and right warp beams cannot always tense the warp yarns completely evenly, and for other reasons. Accordingly, even if the difference between the tensions of warp yarns in opposite end portions of a fabric could be eliminated, the elimination of the difference between the warp tensions in these portion does not always mean the elimination of the difference between the warp tensions in a warp boundary portion.